Multi-aperture image dissector tube

ABSTRACT

An image dissection tube is provided with a plurality of apertures in which each aperture is a different size. Each aperture is associated with an independent photomultiplier channel, and the individual channels are packaged in the same tube. This permits the flexibility possible when different resolutions are desired without having to use several image dissector tubes.

United States Patent Catchpole 1 1March 13, 1973 MULTl-APERTURE IMAGE [56] References Cited DISSECTOR TUBE UNITED STATES PATENTS [751 Invent: Cmhlmle, Southfield, 3,407,324 10/1968 Rome ..313 105 Mich- 3,333,l45 7/1962 Nielsen ..3l5/l0 [73] Assignee: The United States of America as 'f' Exami'fer james Lawrence represented by the Secretary of the Nelms Navy Att0rney-R. S. Scrascra et al.

[22] Filed: Nov. 3, 1971 57 ABSTRACT Appl. No.: 195,326

U.S. Cl ..250/207 R, 313/65 R, 313/103 R Int. Cl. ..H0lj 39/12 Field of Search ..250/207, 213 R, 213 VT;

313/95,103, 104,105, 65 R, 65 A, 65 T OBJECT An image dissection tube is provided with a plurality of apertures in which each aperture is a different size. Each aperture is associated with an independent photomultiplier channel, and the individual channels are packaged in the same tube. This permits the flexibility possible when different resolutions are desired without having to use several image disscctor tubes.

2 Claims, 4 Drawing Figures PATENTED I975 3. 720.838

SHEET 10F 2 OBJECT LENs g FIG. 'I.

FIG. 2.

PATENIEDMAR 1 3 I975 3.720.838

SHEET 2 or 2 FIG. 3..

MULTI-APERTURE IMAGE DISSECTOR TUBE BACKGROUND OF THE INVENTION A conventional image dissector tube comprises a photocathode for emitting an electron image in response to and corresponding to incident radiation. In the usual tube, the electron image is formed and focused into an image plane. A defining or dissecting aperture is located within this image plane, and means are provided for deflecting the beam in a raster pattern or the aperture in generating a time-based video output signal. The electrons pass through the aperture and through an electron multiplier to a target anode from which the video signal may be taken.

The size of the resolving aperture, that is to say the electron transmission cross-section thereof, in part determines the tube sensitivity and resolution characteristics. The larger the aperture, the greater the sensitivity, but the poorer the resolution.

Image dissector tubes are used in a variety of signal processing systems to scan optical images and create therefrom the electrical signals representative of the optical images. In television, for example, an image dissector tube may be employed to pass along an electron analog of a scene to be televised. The electrons of the electron analog pass across a single aperture in a metal plate and the electron passing therethrough constitute a measure of the electron image density and become the output video signal.

In the usual prior art dissector tube only one aperture was provided, but U. S. Pat. No. 3,333,145 issued July 25, l967 to Reinald S. Nielsen discloses a multiplechannel image dissector tube for multiple channel optical image analysis. However, an image dissector tube having a plurality of apertures in which each aperture is a different size is not known in the prior art.

SUMMARY OF THE INVENTION According to the present invention, an image dissector tube is provided with several apertures wherein eachaperture is a different size and each aperture is associated with an independent channel or other electron multiplier. The individual dissecting apertures and channels are packaged in the same tube, thus permitting the flexibility possible when several sensors are used without the bother of having to use several image dissector tubes.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING FIG. 1 is a schematic representation of a dissector tube according to the invention;

FIG. 2 is an elevation view of a three hole aperture plate in accordance with the invention;

FIG. 3 is an enlarged fragmentary cross-sectional view of a portion of the structure of FIG. I;and

FIG. 4 is a simplified schematic diagram of the rear portion of the device of FIG. 1 identifying elements of interest.

DESCRIPTION AND OPERATION The image dissector tube generally indicated at in FIG. 1 employs the usual vacuum enclosure 16 and contains a photocathode 15, an accelerator anode 13. An aperture plate 20 having apertures 21, 22 and 23 connected through channel electron multipliers 31, 32 and 33, and associated output electrodes 41, 42 and 43. Magnetic focus and deflection coils 14 are typically employed outside glass cylinder 16 alternatively electrostatic imaging from photocathode 15 to image plane 20 can also be used as shown in FIG. 4. In operation, an optical image is focused on photocathode l5. Photocathode l5 emits electrons in proportion to the illuminating flux density; hence, an electron replica of the optical image exists in the vicinity of the photocathode. Accelerator anode 13 is held at a potential which is positive in relation to photocathode 15. The positive potential field causes the electrons emitted by the photocathode to be accelerated toward anode l3 and, hence, toward aperture plate 20. An electric current in focus coil 14, for example, is adjusted relative to the electron accelerating potential field, to achieve the condition of focus for electrons arriving at aperture plate 20. Typically, the electron image at photocathode 15 is imaged with unity magnification at aperture plate 20.

The holes in an aperture plate are generally a few thousandths of an inch in diameter ranging typically from about 0.0005 inch to about 0.20 inch.

The present invention contemplates the use of individual channel electron multipliers 31, 32, 33 with at least three different size apertures 21, 22, 23. FIG. 3 in dicates how a bundle can be made of several identical multipliers with coplanar input surfaces with a single metal mask 20 over them. The desired hole size and placement can be accurately made in the mask by known photoetching processes before the plate 20 is welded in place over the channel inputs.

The availability of different size apertures within one image dissector envelope gives several systems advantages without having to resort to using multiple sensors. The field of interest may be examined with high resolution using the smallest aperture when the illumination is adequate. As illumination decreases, so does the apparent field detail and the field of interest may be examined by a larger aperture size consistent with the field resolution. When there is a relative movement between the sensor and the object of interest the object changes in angular size within the field of view. Under these circumstances it is possible to observe the object with a relatively constant degree of detail by progressively scanning the field with the different size apertures. This procedure minimizes the number of picture points which must be processed while tending to maintain maximum signal to noise ratio. If light optics are used in front of the tube the zoom" range thereof is reduced.

Although three round apertures have been shown in the illustrated embodiment, it will be understood that any practical number of apertures of any geometrical configuration may be used without departing from the inventive concept presented.

From the foregoing it may be seen that a versatile image dissector device has been disclosed which is capable of providing information with different resolution capabilities.

What is claimed is:

1. In an image analysis tube comprising:

a photocathode;

means for scanning an electron image formed by said photocathode;

means responsive to electron density at known positures and including apertures of differing, tions of said electron image; distinct fixed sizes for sampling the electron an independent signal channel means for each of said mag adjacent electron density responsive means;and The tube accordmg Clalm 1 Wheffim Sald ad t means; 5 readout means includes apertures of at least three the improvement comprising: dlstmct SlZeS- said readout means including a plurality of aper- I 

1. In an image analysis tube comprising: a photocathode; means for scanning an electron image formed by said photocathode; means responsive to electron density at known positions of said electron image; an independent signal channel means for each of said adjacent electron density responsive means; and readout means; the improvement comprising: said readout means including a plurality of apertures and including apertures of differing, distinct fixed sizes for sampling the electron image.
 1. In an image analysis tube comprising: a photocathode; means for scanning an electron image formed by said photocathode; means responsive to electron density at known positions of said electron image; an independent signal channel means for each of said adjacent electron density responsive means; and readout means; the improvement comprising: said readout means including a plurality of apertures and including apertures of differing, distinct fixed sizes for sampling the electron image. 